SCons Developer's Guidelines

8 December 2014

General

All SCons software (SCons itself, tests, supporting utilities) will be
written to work with Python version 2.7.

SCons will be tested against Python versions
2.7 and all later versions of 2.x.
(As of this writing, SCons does not support Python 3.x,
as the syntax has changed sufficiently
that a single source will not support both.)

The SCons distribution will be generated
by the distutils package.

SCons will not require installation of any additional Python modules or
packages. All modules or packages used by SCons must either be part of
the standard Python
2.7
release or be part of the SCons distribution.

SCons installation will be atomic, and will install all necessary
non-standard modules and/or packages.

At a minimum, SCons will be tested on Linux and Windows XP. We will add
other platforms as they become available. All tests must be written
portably.

SCons software will be written to a separately-defined set of
conventions (variable naming, class naming, etc.). We won't be dogmatic
about these, and will use discretion when deciding whether a naming
violation is significant enough to require a fix.

SCons is being developed using the following source code
control system(s):

QMTest is the default driver for all tests. Individual tests
are written using the following infrastructure pieces:

SCons infrastructure module tests are written using PyUnit.

Tests of SCons packaging are written using subclasses of the
TestCmd.py module.

Tests of full SCons script functionality are written using subclasses
of the TestCmd.py module.

Development philosophy

In a word (x3): Testing, testing, testing.

We're growing a rich set of regression tests incrementally, while
SCons is being developed. The goal is to produce an exceptionally
stable, reliable tool of known, verifiable quality right from the
start.

A strong set of tests allows us to guarantee that everything works
properly even when we have to refactor internal subsystems, which we
expect to have to do fairly often as SCons grows and develops. It's
also great positive feedback in the development cycle to make a change,
see the test(s) work, make another change, see the test(s) work...

Testing methodology

The specific testing rules we're using for SCons are as follows:

Every functional change must have one or more new tests, or
modify one or more existing tests.

The new or modified test(s) must pass when run against your new
code (of course).

The new code must also pass all unmodified, checked-in tests
(regression tests).

The new or modified test(s) must fail when run against the
currently checked-in code. This verifies that your new or
modified test does, in fact, test what you intend it to. If
it doesn't, then either there's a bug in your test, or you're
writing code that duplicates functionality that already exists.

Changes that don't affect functionality (documentation changes,
code cleanup, adding a new test for existing functionality,
etc.) can relax these restrictions as appropriate.

These rules are taken from the Aegis change management system, which
SK uses behind the scenes to manage SCons integrations
(and his personal development process).

The SCons testing infrastructure is largely in place, and is intended
to make writing tests as easy and painless as possible. We will change
the infrastructure as needed to continue to make testing even easier, so
long as it still does the job.

SCons development uses three (!) testing harnesses, one for unit tests,
one for end-to-end functional tests, and one for test execution:

The infrastructure modules (under the src/scons
subdirectory) all have individual unit tests that use PyUnit.
The naming convention is to append "Tests" to the
module name. For example, the unit tests for the
src/scons/Foo.py module can be
found in the src/scons/FooTests.py file.

The packaging is tested by test scripts
that live in the src/ subdirectory
and use a prefix of "test_".

The scons utility itself is tested by end-to-end tests that
live in the test/ subdirectory and which use the
TestCmd.py infrastructure.

Execution of these tests will be handled by the
QMTest
infrastructure, as wrapped by an execution script.
Note: The transition to using
QMTest is still in progress. The wrapper execution script
currently executes the test scripts directly.

The end-to-end tests in the test/ subdirectory are
not substitutes for module unit tests. If you modify a module
under the src/scons/ subdirectory, you generally
mustmodify its *Tests.py script to
validate your change. This can be (and probably should be) in addition to
a test/* test of how the modification affects the end-to-end
workings of SCons.

General developer requirements

All project developers must subscribe to the dev@scons.tigris.org
mailing list.

All project developers must register at Tigris.org and be added to the
SCons developer list, so that the number of active developers can be
accurately represented on the SCons project page.

We will accept patches from developers not actually registered on
the project, so long as the patches conform to our normal requirements.

Using Mercurial for SCons development

Developers using Mercurial may, but need not,
be registered at Bitbucket.org, and should submit pull
requests to
the SCons Bitbucket account.